Triallelic digenic mutation in the prokineticin 2 and GNRH receptor genes in two brothers with normosmic congenital hypogonadotropic hypogonadism

Gonadotropin-Releasing Hormone Receptor (GnRHR) and Hypogonadotropic Hypogonadism

Human sexual and reproductive development is regulated by the hypothalamic-pituitary-gonadal (HPG) axis, which is primarily controlled by the gonadotropin-releasing hormone (GnRH) acting on its receptor (GnRHR). Dysregulation of the axis leads to conditions such as congenital hypogonadotropic hypogonadism (CHH) and delayed puberty. The pathophysiology of GnRHR makes it a potential target for treatments in several reproductive diseases and in congenital adrenal hyperplasia. GnRHR belongs to the G protein-coupled receptor family and its GnRH ligand, when bound, activates several complex and tissue-specific signaling pathways. In the pituitary gonadotrope cells, it triggers the G protein subunit dissociation and initiates a cascade of events that lead to the production and secretion of the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) accompanied with the phospholipase C, inositol phosphate production, and protein kinase C activation. Pharmacologically, GnRHR can be modulated by synthetic analogues. Such analogues include the agonists, antagonists, and the pharmacoperones. The agonists stimulate the gonadotropin release and lead to receptor desensitization with prolonged use while the antagonists directly block the GnRHR and rapidly reduce the sex hormone production. Pharmacoperones include the most recent GnRHR therapeutic approaches that directly correct the misfolded GnRHRs, which are caused by genetic mutations and hold serious promise for CHH treatment. Understanding of the GnRHR's genomic and protein structure is crucial for the most appropriate assessing of the mutation impact. Such mutations in the GNRHR are linked to normosmic hypogonadotropic hypogonadism and lead to various clinical symptoms, including delayed puberty, infertility, and impaired sexual development. These mutations vary regarding their mode of inheritance and can be found in the homozygous, compound heterozygous, or in the digenic state. GnRHR expression extends beyond the pituitary gland, and is found in reproductive tissues such as ovaries, uterus, and prostate and non-reproductive tissues such as heart, muscles, liver and melanoma cells. This comprehensive review explores GnRHR's multifaceted role in human reproduction and its clinical implications for reproductive disorders.

Therapeutic Potential of Targeting Prokineticin Receptors in Diseases

The prokineticins (PKs) were discovered approximately 20 years ago as small peptides inducing gut contractility. Today, they are established as angiogenic, anorectic, and proinflammatory cytokines, chemokines, hormones, and neuropeptides involved in variety of physiologic and pathophysiological pathways. Their altered expression or mutations implicated in several diseases make them a potential biomarker. Their G-protein coupled receptors, PKR1 and PKR2, have divergent roles that can be therapeutic target for treatment of cardiovascular, metabolic, and neural diseases as well as pain and cancer. This article reviews and summarizes our current knowledge of PK family functions from development of heart and brain to regulation of homeostasis in health and diseases. Finally, the review summarizes the established roles of the endogenous peptides, synthetic peptides and the selective ligands of PKR1 and PKR2, and nonpeptide orthostatic and allosteric modulator of the receptors in preclinical disease models. The present review emphasizes the ambiguous aspects and gaps in our knowledge of functions of PKR ligands and elucidates future perspectives for PK research. SIGNIFICANCE STATEMENT: This review provides an in-depth view of the prokineticin family and PK receptors that can be active without their endogenous ligand and exhibits "constitutive" activity in diseases. Their non- peptide ligands display promising effects in several preclinical disease models. PKs can be the diagnostic biomarker of several diseases. A thorough understanding of the role of prokineticin family and their receptor types in health and diseases is critical to develop novel therapeutic strategies with safety concerns.

Oligogenic Inheritance Underlying Incomplete Penetrance of PROKR2 Mutations in Hypogonadotropic Hypogonadism

The role of the prokineticin 2 pathway in human reproduction, olfactory bulb morphogenesis, and gonadotropin-releasing hormone secretion is well established. Recent studies have highlighted the implication of di/oligogenic inheritance in this disorder. In the present study, we aimed to identify the genetic mechanisms that could explain incomplete penetrance in hypogonadotropic hypogonadism (HH). This study involved two unrelated Tunisian patients with HH, which was triggered by identifying a homozygous p.(Pro290Ser) mutation in the PROKR2 gene in a girl (HH1) with Kallmann syndrome (KS). The functional effect of this variant has previously been well demonstrated. Unexpectedly, her unaffected father (HH1P) and brother (HH1F) also carried this genetic variation at a homozygous state. In the second family, we identified a heterozygous p.(Lys205del) mutation in PROKR2, both in a male patient with normosmic idiopathic IHH (HH12) and his asymptomatic mother. Whole-exome sequencing in the three HH1 family members allowed the identification of additional variants in the prioritized genes. We then carried out digenic combination predictions using the oligogenic resource for variant analysis (ORVAL) software. For HH1, we found the highest number of disease-causing variant pairs. Notably, a CCDC141 variant (c.2803C > T) was involved in 18 pathogenic digenic combinations. The CCDC141 variant acts in an autosomal recessive inheritance mode, based on the digenic effect prediction data. For the second patient (HH12), prediction by ORVAL allowed the identification of an interesting pathogenic digenic combination between DUSP6 and SEMA7A genes, predicted as “dual molecular diagnosis.” The SEMA7A variant p.(Glu436Lys) is novel and predicted as a VUS by Varsome. Sanger validation revealed the absence of this variant in the healthy mother. We hypothesize that disease expression in HH12 could be induced by the digenic transmission of the SEMA7A and DUSP6 variants or a monogenic inheritance involving only the SEMA7A VUS if further functional assays allow its reclassification into pathogenic. Our findings confirm that homozygous loss-of-function genetic variations are insufficient to cause KS, and that oligogenism is most likely the main transmission mode involved in Congenital Hypogonadotropic Hypogonadism.

The novel function of miR-3195 for mutant PROK2 (c.223-4C>A) degradation

Kallmann syndrome (KS) is a rare human genetic disorder characterized by hypogonadotropic hypogonadism with the reduction or absence of olfactory sense. Mutations in multiple genes, including chemokine prokineticin-2 (PROK2), are considered to contribute to the abnormal migration of gonadotropin-releasing hormone neurons in the embryonic stage. However, the mechanisms of the different inheritance modes of KS have not been comprehensively determined. In this article, we present the case of one KS patient with the same mutation in PROK2 (c.223-4C>A) as his mother. RNA sequencing analysis of his leukocytes showed a new transcript of PROK2, which contained a partial intron (192 bp) compared to those of his parents. Furthermore, we observed that hsa-miR-3195 was expressed at low levels in his and his father's sera compared to his mother's. Unexpectedly, hsa-miR-3195 was also identified to specifically target the 192 bp intron of the aberrant PROK2 transcript of this patient. We determined that high expression of hsa-miR-3195 could efficiently target aberrant PROK2 and stabilize the normal function of PROK2 in vitro, which provided a probable explanation for the different phenotypes of the patient and his mother with the same genotype.

Identification of two novel mutations in three Chinese families with Kallmann syndrome using whole exome sequencing

Kallmann syndrome (KS) is a rare developmental disorder that manifests as congenital hypogonadotropic hypogonadism with anosmia. More than 19 genes have been found to be associated with KS. However, approximately 70% of the causes of KS remain unclear. Here, we studied seven KS patients, from three families, who had delayed puberty and olfactory bulb dysplasia. However, the families of these patients showed a range of other unique clinical features, including hearing loss, anosmia (to varying degrees) and unilateral renal agenesis. We performed whole exome sequencing and copy number variation (CNV) sequencing on samples acquired from these patients. We identified two novel mutations (c.844delC in ANOS1, c.475C>T in SOX10) and a novel trigenic pattern, PROKR2/CHD7/FEZF1 (c.337T>C in PROKR2, c.748C>G in FEZF1, c.8773G>A in CHD7). The c.844delC mutation in the ANOS1 gene was predicted to generate a truncated form of the anosmin-1 protein. SIFT and PolyPhen-2 predicted that the c.475C>T mutation in SOX10 had a damaging effect. The PROKR2 mutation (c.337T>C) was previously reported as harmful. No pathogenic copy number alterations were detected. Our study expands the genotypic and phenotypic spectrum of KS, a disease that shows considerable clinical and genetic heterogeneity. The application of whole exome sequencing could facilitate our understanding of the pathogenesis of KS.

COQ8A and MED25 Mutations in a Child with Intellectual Disability, Microcephaly, Seizures, and Spastic Ataxia: Synergistic Effect of Digenic Variants?

We report on a girl, born to first-cousin Lebanese parents, with severe intellectual disability, congenital hip luxation, cardiac malformation, short stature, facial dysmorphic features including microcephaly, sparse hair, bilateral epicanthal folds, ataxia, seizures, and elevated lactate and pyruvate levels in serum. Whole exome sequencing was carried out on the patient's DNA. Potentially causal homozygous variants in the MED25 (p.Ile173Thr) and COQ8A (p.Arg512Trp) genes were found. The potential pathogenicity of these variants, and the possibility that the 2 variants could synergistically act to produce the phenotype reported, is discussed.